Answer:
These are called Sankey Diagrams.
These summarise all the energy transfers taking place in a process. Sankey diagrams are drawn to scale - the thicker the line or arrow, the greater the amount of energy involved. Usually, the top line/arrow shows the amount of useful energy transferred from the total input and the one which curves shows the wasted/dissipated energy of the total input energy. It helps to show efficiency in this manner.
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